Newer diesel engines emit more harmful nanoparticles

Low-emission diesel engines emit nanoparticles that could be more harmful to human health than the dark exhaust fumes produced by older models, a study by researchers in Germany and Italy has found.

Nanoparticles from newer diesel engines are 5-20nm across and penetrated lung tissue more deeply than older engine exhaust particles, which are around twice as large.

In vitro tests, by researchers at the Max Planck Society's Fritz Haber Institute in Berlin and the Institute of Neurobiology and Molecular Medicine in Rome, also showed that the nanoparticles emitted from diesel engines conforming to 2005 Euro-IV low emission standards kill substantially more white blood cells.

Dangsheng Su of the Fritz Haber Institute's department of inorganic chemistry says that the damaging effects of the Euro-IV particles could be due to the optimised combustion conditions in low-emission engines.

The new engines almost completely burn the diesel, while in older engines small amounts of unburned fuel lead to more - and bigger - soot particles.

Soot particles from Euro-IV diesel engines also have a strongly defective structure and a high abundance of chemically reactive surface elements, says Su. Furthermore, the hydrophilic surface chemistry of Euro-IV soot particles from attached OH groups allow facile chemical and morphological contact with hydrophilic biomolecules. Soot particles from older engines, on the other hand, are hydrophobic with smooth, inert surfaces.

Burning issue

Su says the only way answer to the problem available at the moment is better filtering exhaust fumes from Euro-IV engines. 'From the point of view of physical chemistry, you cannot completely burn off the fuel in an unstationary engine,' he said. 'To do that you would need much more combustion time and a much higher concentration of oxygen.'

Justin Lingard, of the School of Earth and Environment at the University of Leeds in the UK, notes that the team had based the study on bigger engines normally used in utility vehicles. 'If the observations can be transferred to automobiles, this would be cause for concern,' he says.

Lingard adds that exhaust fumes contain a mix of different particles but there is little in the paper to say which of these might be causing the damage to cells.

He also points out that the team looked at undiluted exhaust fumes at 200°C and not under 'real-world' conditions. 'High temperature sampling may promote surface modification, both chemical and physical, when compared to a particle sampled at the roadside,' he says.